1. Field of the Invention
The present invention relates to a mobile station identification system and, more particularly, to a method of using an international mobile station identity (IMSI) to identify a mobile communications device (i.e., a mobile station) to a base station in a mobile communications network.
2. Discussion of the Related Art
In the world of cellular telecommunications, those skilled in the art often use the terms 1G, 2G, and 3G. The terms refer to the generation of the cellular technology used. 1G refers to the first generation, 2G to the second generation, and 3G to the third generation.
1G is used to refer to the analog phone system, known as an AMPS (Advanced Mobile Phone Service) phone systems. 2G is commonly used to refer to the digital cellular systems that are prevalent throughout the world, and include CDMAOne, Global System for Mobile communications (GSM), and Time Division Multiple Access (TDMA). 2G systems can support a greater number of users in a dense area than can 1G systems.
3G is commonly used to refer to the digital cellular systems currently being developed. Recently, third-generation (3G) CDMA communication systems have been proposed including proposals, such as cdma2000 and W-CDMA. These 3G communication systems are conceptually similar to each other with some significant differences.
A cdma2000 system is a third-generation (3G) wideband, spread spectrum radio interface system which uses the enhanced service potential of CDMA technology to facilitate data capabilities, such as Internet and intranet access, multimedia applications, high-speed business transactions, and telemetry. The focus of cdma2000, as is that of other third-generation systems, is on network economy and radio transmission design to overcome the limitations of a finite amount of radio spectrum availability.
FIG. 1 illustrates a cdma2000 network architecture, wherein a subscriber uses a mobile communications device or a Mobile Station (MS) to access network services. The Mobile Station may be a portable communications unit, such as a hand-held cellular phone, a communication unit installed in a vehicle, or even a fixed-location communications unit.
The electromagnetic waves from the Mobile Station are transmitted by the Base Transceiver System (BTS) also known as node B. The BTS consists of radio devices such as antennas and equipment for transmitting radio waves. The Base Controller Station (BSC) receives the transmissions from one or more BTS's. The BSC provides control and management of the radio transmissions from each BTS by exchanging messages with the BTS and the Mobile Switching Center (MSC) or Internal IP Network. The BTS's and BSC are part of the Base Station (BS).
The BS exchanges messages with and transmits data to a Circuit Switched Core Network (CSCN) and Packet Switched Core Network (PSCN). The CSCN Provides traditional voice communications and the PSCN provides data communications for Internet applications and multimedia services.
The Mobile Switching Center (MSC) portion of the CSCN provides switching for traditional voice communications to and from an Mobile Station and may store information to support these capabilities. The MSC may be connected to one or more BS's as well as other public networks, for example a Public Switched Telephone Network (PSTN) or Integrated Services Digital Network (ISDN). A Voice Location Register (VLR) is used to retrieve information for handling voice communications to or from a visiting subscriber. The VLR may be within the MSC and may serve more than one MSC.
A user identity is assigned to the Home Location Register (HLR) of the CSCN for record purposes such as subscriber information, for example Electronic Serial Number (ESN), Mobile Directory Number (MDR), Profile Information, Current Location, and Authentication Period. The Authentication Center (AC) manages authentication information related to the Mobile Station. The AC may be within the HLR and may serve more than one HLR. The interface between the SC and the HLR/AC is an IS-41 standard interface.
The Packet Data Serving Node (PDSN) portion of the PSCN provides routing for packet data traffic to and from Mobile Station. The PDSN establishes, maintains, and terminates link layer sessions to the Mobile Station's and may interface with one of more BS and one of more PSCN.
The Authentication, Authorization and Accounting (AAA) Server provides Internet Protocol authentication, authorization and accounting functions related to packet data traffic. The Home Agent (HA) provides authentication of MS IP registrations, redirects packet data to and from the Foreign Agent (FA) component of the PDSN, and receives provisioning information for users from the AAA. The HA may also establish, maintain, and terminate secure communications to the PDSN and assign a dynamic IP address. The PDSN communicates with the AAA, HA and the Internet via an Internal IP Network.
FIG. 2 shows a layered architecture diagram of the cdma2000 system. Layered architecture is a form of hierarchical modularity used in data network design. All major emerging communication network technologies rest on the layers of the International Organization for Standardization (ISO/OSI) model, illustrated in FIG. 2. A layer performs a category of functions or services. The OSI model defines a Physical Layer 20 (Layer-1) which specifies the standards for the transmission medium, a Link Layer 30 (Layer-2), a Network Layer 40 (Layer-3) which implements routing and flow control for the network, a Transport Layer 50 (Layer-4) and Upper Layers 60 (Layers-5 to 7).
Link Layer 30 and Data Link Protocols (DLP) are used to mitigate the effects of impairments introduced by the physical transmission medium. A Radio Link Protocol (RLP) is designed for the wireless system to deal specifically with the types of impairments found on the radio link and comprises mechanisms to deal with errors on the communications link, delays encountered in transmitting information, lost information, bandwidth conservation, and contention resolution.
The Transport Layer 50 provides reliable and transparent transfer of data between end points. It provides end-to-end error recovery and flow control. For the Internet based protocol model, the Transport Control Protocol (TCP) mainly corresponds to the Transport Layer of the OSI model.
Referring to FIG. 3, a data link protocol architecture layer for a wireless network, and more particularly for a cdma2000 system is provided. The upper layers 60, corresponding to Layer-5 to 7, contain three basis services; voice services, end-user data-bearing services and signaling. Voice services 62 include PSTN access, mobile-to-mobile voice services, and Internet telephony. End-user data-bearing services are services that deliver any form of data on behalf of a mobile end user and include packet data applications (e.g., IP service) 61, circuit data applications (e.g., asynchronous fax and B-ISDN emulation services) 63, and SMS. Signaling services control all aspects of mobile operation.
Voice services 62 may utilize directly the services provided by the LAC services. Signaling services 70 are illustrated over layers 40, 50 and 60 to indicate that the signaling information is exchanged between all layers corresponding to Layer-3 to 7.
The Transport Layer 50, corresponding to Layer-4, includes the Transport Control Protocol (TCP) 51 and the User Datagram Protocol (UDP) 52. A Hyper Text Transport Protocol (HTTP), a Real-time Transport Protocol (RTP), or other protocols may also be present.
The Link Layer 30, corresponding to Layer-2, is subdivided into the Link Access Control (LAC) sublayer 32 and the Medium Access Control (MAC) sublayer 31. The link layer provides protocol support and control mechanisms for data transport services and performs the functions necessary to map the data transport needs of the upper levels 60 into specific capabilities and characteristics of the physical layer 20. The Link Layer may be viewed as an interface between the upper layers and the Physical Layer 20.
The separation of MAC 31 and LAC 32 sublayers is motivated by the need to support a wide range of upper layer services, and the requirement to provide for high efficiency and low latency data services over a wide performance range (from 1.2 Kbps to greater than 2 Mbps). Other motivators are the need for supporting high QoS delivery of circuit and packet data services, such as limitations on acceptable delays and/or data BER (bit error rate), and the growing demand for advanced multimedia services each service having a different QoS requirements.
The LAC sublayer 32 is required to provide a reliable, in-sequence delivery transmission control function over a point-to-point radio transmission link 42. The LAC sublayer manages point-to point communication channels between upper layer entities and provides framework to support a wide range of different end-to-end reliable link layer protocols.
The MAC sublayer 31 facilitates complex multimedia, multi-services capabilities of 3G wireless systems with Quality of Service (QoS) management capabilities for each active service. MAC Control States 35 includes procedures for controlling the access of data services (packet and circuit) to the physical layer 20, including the contention control between multiple services from a single user, as well as between competing users in the wireless system.
Best Effort Delivery 33 provides for reasonably reliable transmission over the radio link layer using a Radio Link Protocol (RLP) for a best-effort level of reliability. Multiplexing and Quality of Service (QoS) Control 34 is responsible for enforcement of negotiated QoS levels by mediating conflicting requests from competing services and the appropriate prioritization of access requests.
The Physical Layer 20, corresponding to Layer-1, is responsible for coding and modulation of data transmitted over the air. The Physical Layer 20 conditions digital data from the higher layers so that the data may be transmitted over a mobile radio channel reliably. The Physical Layer 20 maps user data and signaling, which are delivered by the MAC sublayer 31 over multiple transport channels, into a physical channels and transmits the information over the radio interface. In the transmit direction, the functions performed by the Physical Layer 20 include channel coding, interleaving, scrambling, spreading and modulation. In the receive direction, the functions are reversed in order to recover the transmitted data at the receiver.
The International Telecommunications Union (ITU) originally spearheaded the 3G (Third Generation) standard for mobile communications systems, pursuant to the International Mobile Telephony 2000 (IMT2000) project. IMT2000 provides a vision for a single global standard for wireless networks perceived as the global 3G system. In a 3G system, the next generation of mobile communications systems will offer enhanced services, such as multimedia and video. The main 3G technologies include Universal Mobile Telecommunications System (UMTS) and CDMA2000™.
UMTS provides an enhanced range of multimedia services. UMTS will speed convergence between telecommunications, information technology, media and content industries to deliver new services and create fresh revenue generating opportunities. UMTS will deliver low cost, high capacity mobile communications offering data rates as high as 2 Mbps under stationary conditions with global roaming and other advanced capabilities. The specifications defining UMTS are formulated by Third Generation Partnership Project (3GPP).
The CDMA2000™ standards family defines the use of Code Division Multiple Access (CDMA) technology to meet the requirements for 3G wireless communication systems. These standards have been developed through comprehensive proposals from Qualcomm. CDMA2000 was one of the first 3G IMT-2000 technologies to be commercially deployed, in late 2000. It offers twice the voice capacity and data speed (up to 307 Kbps) on a single 1.25 MHz (1X) carrier in a new or an existing spectrum. CDMA2000 1X is also known as IS-2000, MC-1X and IMT-CDMA MultiCarrier 1X and 1xRTT. The specifications defining CDMA2000 are formulated by Third Generation Partnership Project 2 (3GPP2).
International Telecommunications Union-Telecommunication Standardization Sector (ITU-T) is an international body that develops worldwide standards for telecommunications technologies. These standards are grouped together in series, which are prefixed with a letter indicating the general subject and a number specifying the particular standard. ITU-T Series E, for example, deals with the overall network operation, telephone service, service operation and human factors. Particularly, ITU-T E.212 provides for an International Mobile Subscriber Identity (IMSI).
IMSI is a unique identifier allocated to each mobile subscriber in a GSM and UMTS network. IMSI includes a Mobile Country Code (MCC), a Mobile Network Code (MNC) and a Mobile Station Identification Number (MSIN), as illustrated in FIG. 4. MCC is a 3-digit number uniquely identifying a given country. MNC is either a 2 or 3-digit number used to uniquely identify a given network from within a specified country. MNC is used in identifying various networks in a country using the same MCC.
The manufacturer typically assigns the MSIN. The MSIN comprises a maximum of 10 digits, and is used in identifying a mobile communications device or a mobile station in each network using the same MNC. The combination of the MNC and the MSIN is referred to as national mobile station identity (NMSI), which uniquely identifies a mobile station within its home country.
Generally, an IMSI is constructed with maximum 15 digits. IMSI as illustrated in FIG. 4 is used for assigning an internationally generic identifier number to a mobile station. Hence, even when a mobile station is roaming internationally, a servicing base station or communications network can determine in which network and country a mobile station is registered, based on the values of MCC and MNC. Thus, IMSI simplifies and facilitates billing practices in a roaming network, whether locally or internationally.
In the cdma2000 system, IMSI is classified into two types. A first type is class 0 IMSI and the other is class 1 IMSI. Class 0 IMSI has 15 digits, wherein class 1 IMSI has digits less than fifteen. Referring to FIG. 5, a class 1 IMSI is illustrated. IMSI includes a MCC and an IMSI_S, wherein the MCC field coincides with 11th and 12th digits of IMSI (IMSI—11—12). As shown, in this example, the overall length of IMSI is 13 digits. MNC and MSIN fields are 2 digits and 8 digits, respectively. Thus, the length of IMSI_S of cdma2000 is 10 digits. Hence, IMSI—11—12 coincides with the least two significant digits of MCC.
Typically, IMSI_S corresponds to MSIN as provided in ITU-T E.212 and is constructed with 10 digits. If MSIN is 10 digits, IMSI_S is constructed with 10 digits. If MSIN is less than 10 digits, however, or if the overall length of IMSI is 10 digits or is greater than 10 digits, IMSI_S includes the least significant 10 digits of the IMSI. Referring to FIGS. 6 to 8, other exemplary class 1 IMSI structures are illustrated, wherein IMSI—11—12 fails to coincide with the MNC field as recommended in ITU-T E.212.
Referring to FIG. 6, the overall length of IMSI is 12 digits. MNC and MSIN are 2 digits and 5 digits, respectively, and MCC is 3 digits. Hence, in order to meet the overall length of IMSI equal to 12 digits, padding bits (e.g., zero bits) are provided to fill the 2 most significant positions, provided here as IMSI—11—12. As such, in this case, since the length of IMSI_S of cdma2000 is 10 digits, IMSI—11—12 is padded with padding bits to provide the total length of 12 digits.
Referring to FIG. 7, if MNC and MSIN are 3 digits and 7 digits, respectively, the length of IMSI_S of cdma2000 is 10 digits. Hence, IMSI—11—12 coincide with the least two significant digits of MCC.
Referring to FIG. 8, if MNC and MSIN are 3 digits and 4 digits, respectively, the MCC is 3 digits. Hence, in order to meet the 12-digit length, padding bits are added in the most significant position of the IMSI. In this case, since length of IMSI_S of cdma2000 is 10 digits, IMSI—11 and IMSI—12 include a padding digit each.
A problem is associate with the above padding method, however. That is, according to provisions of ITU-T E.212, the IMSI—11—12 should coincide with the MNC field. This coincidence would enable a base station in the cdma2000 system to easily determine the network and country to which a mobile station belongs. A solution to the above problem is needed.